72 DARK GROUND ILLUMINATION WITH HIGH POWERS [Ch. II 



§ 126. Experiments with high powers and dark field. — Put the 

 special dark-ground illuminator (fig. 50) in place of the condenser 



Fig. 49. Small Arc Lamp and Connections. 

 (From Optic Projection). 



A Small arc lamp base with right-angle carbons (HC, VC) with insulation 

 (In. In). 



The arc and the condenser (C) are in position to give a parallel beam. 



Ch Chimney over the arc, T, tube holding the condenser; sli, metal shield 

 at the end of the condenser tube. 



W 1 Wire cable to the lamp socket (So) with its key switch (K). 



Sp Separable plug. 



W 2, W 3 Wire to the upper or horizontal carbon (H C). 



W 4 Wire to the rheostat (R) and to the lower or vertical carbon (V C). 



C Tips of carbons for alternating current. 



D Tips of carbons for direct current, the positive pole always being on 

 the horizontal carbon (+), and the negative pole on the lower or vertical car- 

 bon (-). 



E Shield at the end of the condenser tube; the face of the condenser is 

 shown at (C). 



ordinarily used. Push it upward in the sleeve so that it can be brought 

 by the screw flush with the upper surface of the stage. Use a 16 mm. 



